Mark R. Segal and Jacob W. Segal

The recent (April 25, 2018) second data release (DR2) of the European Space Agency satellite Gaia provides a dramatic increase in the extent and precision of stellar attributes for an unprecedented number of sources in the Milky Way (MW). For instance, data on position in the sky and proper motion are available for more than 1.3 billion stars, with a subset of more than 7 million of the brightest stars having radial velocity measurements. (Definitions of proper motion, radial velocity, and other astronomical terms are provided in the glossary.)

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